Solid-liquid phase interfacial polymerization processes are closely related to liquid-liquid phase interfacial polymerization processes, and both techniques have been used to produce polycondensation polymers. The conventional liquid-liquid phase interfacial polymerization process is a polycondensation reaction wherein monomers are dissolved in mutually immiscible solvents. Polymerization occurs when the monomer in one phase diffuses from the bulk of the solution into the interface, and reacts with the monomer in the other phase.
A solid-liquid phase interfacial polymerization process is slightly different, however, but achieves similar results. Thus, the solid-liquid phase process involves a polymerization reaction wherein one monomer is dissolved in a solvent to form a liquid phase. However, the other phase is not liquid, but rather a solid, and the polycondensation reaction occurs at the liquid phase-solid phase interface.
As is true for liquid-liquid phase interfacial polymerization, solid-liquid phase polymerization rates depend upon the diffusion rate and the reactivity of functional groups on the monomers. The particle size of the solid phase monomer can also influence overall polymerization rates.
One example of known solid-liquid phase interfacial polymerization processes is the synthesis of polycarbonate polymers, which involves the reaction of potassium carbonate as the solid phase monomer, and dibromo-p-xylene dissolved in a solvent, as the liquid phase. This reaction has been variously described in the literature, including the Journal of Polymer Science, Polymer Chemistry Edition, Volume 17, Page 517, (1979); Polymer Preprints, American Chemical Society, Division of Polymer Chemistry, Volume 22, No. 2, Page 387, (1981); and Polymer Preprints, American Chemical Society, Division of Polymer Chemistry, Volume 23, No. 2, Page 174, (1982).
Among the conventional liquid-liquid phase interfacial polymerization reactions are the polycondensation of diamines with a diacetyl chloride to form nylon, i.e., polyamides; and the reaction of alcohols with acids to form polyesters. Interfacial polymerization processes in the organic realm typically provide advantages such as faster polymerization rates than other types of polymerization reactions such as bulk or solution polymerization. Even more important, however, is the fact that because stoichiometry between monomers need not be precise, a higher molecular weight polymer can be obtained by these methods. This is particularly important in organic polycondensation reactions where an imbalance of a fraction of a percent can cause the extent of polymerization to be greatly affected.
Another advantage of the interfacial polymerization process is that it can result in the formation of high molecular weight polymers at an interface, regardless of the overall percent conversion of bulk amounts of the two or more monomeric reactants remaining in the solution.
Further advantages offered by interfacial polymerization reactions in the synthesis of organic polymers include (i) the ability to prepare infusible polymers; (ii) the ability to synthesize polymers with chemically active substituents as well as heteroatoms; (iii) the ability to control the crosslinking of the polymer structure; (iv) the ability to use cis- and trans-conformation without rearrangement; (v) the ability to prepare optically active polymers without decomposition of intermediates; (vi) the ability to use short-chain and/or substituted ring intermediates; (vii) the ability to use thermally unstable intermediates to form thermally stable polymers; (vii) the ability to form block and ordered copolymeric structures; (ix) the ability to form synthetic elastomers; (x) it offers a direct method of forming polymer solutions and dispersions; (xi) it provides a direct method for the polymerization and formation of polymer coatings and encapsulants; and (xii) it is a direct method for polymerization of monomers into fibrous particulates, fibers, and films.
A significant additional advantage of a solid-liquid phase, interfacial polymerization process involving a silicon atom containing monomer, is the ability to control the structure of the resulting polymer chain and the composition of the resulting copolymers, without requiring the use of a catalyst, and without the usual problems associated with various rearrangements which occur during such equilibrium polymerization processes.
Accordingly, and with respect to the present invention, a non-aqueous, solid-liquid phase interfacial polymerization process can be carried out by using a dihaloorganosilane or a dihaloorganosiloxane dissolved in solvent to form the liquid phase. A solventless, solid, alkali metal silanolate or an alkali metal siloxanolate, is used as the other phase. High molecular weight polysiloxanes and alkali metal chloride salts are formed at the solid-liquid interface.
When a dihaloorganosilane is used as the liquid phase, or when an alkali metal silanolate is used as the solid phase in the reaction, then a single silicon atom containing repeating unit will form. When a dihaloorganosiloxane is used as the liquid phase, or when an alkali metal siloxanolate is used as the solid phase in the reaction, then a multi-silicon atom containing repeating unit will form, e.g., a trisiloxane repeating unit.
Since the inorganic salt by-product of the reaction, i.e., the alkali metal chloride, is not soluble in the organic solvent phase, it separates from the solution, and hence does not interfere with the polycondensation reaction. If the polymer is insoluble in the solvent phase, it also phase separates from the reaction zone. The separated polymer and inorganic salt can then be washed several times with distilled or deionized water, to remove the inorganic salt and any unreacted silanolate or siloxanolate salts. If the polymer is soluble in the organic solvent phase, it can be removed by any suitable extraction procedure, such as filtration and evaporation of solvent, or by polymer precipitation via addition of an incompatible solvent. Washing of the resulting polymer with distilled water removes any residual inorganic salt and any unreacted silanolate or siloxanolate salt.